Prevention of Staphylococcus aureus burn wound colonization by nasal mupirocin

BACKGROUND: There are two important routes for the transmission of Staphylococcus aureus to the burn wound. In the endogenous route, patients naturally carrying S. aureus colonize their own wounds, whereas in the exogenous route burn wounds are cross-infected from other sources. In this study we evaluated the effect of blocking the endogenous route on S. aureus burn wound colonization by mupirocin application in the nose of patients at the time of admission. METHODS: From September 2000 to January 2002 all patients with burns admitted to a single dedicated Burn Centre received nasal mupirocin upon admission. This period was compared to two control periods (C1: July 1999 to July 2000 and C2: January 2002 to January 2003) for S. aureus burn wound colonization. The colonization risk was analysed, adjusting for confounding, with Cox proportional hazard regression. RESULTS: A total of 98 patients did not have S. aureus burn wound colonization at the time of admission and were, thus, considered at risk for S. aureus acquisition during their stay. As compared to C1, the relative risk of acquiring S. aureus in their wound was 0.48 (95% CI: 0.24-0.97) in the mupirocin period and 0.55 (95% CI: 0.28-1.1) during the C2 period. S. aureus nasal/pharyngeal colonization was a significant independent risk factor for wound colonization (RR: 2.3; 95% CI: 1.2-4.2). CONCLUSION: Nasal mupirocin may contribute to risk reduction of S. aureus wound colonization in patients with burns.     

Molecular epidemiology of Pseudomonas aeruginosa, Burkholderia cepacia complex and methicillin-resistant Staphylococcus aureus in a cystic fibrosis center.

Chronic pulmonary infections caused by Pseudomonas aeruginosa, Burkholderia cepacia complex and Staphylococcus aureus are responsible for most of the morbidity and mortality of patients with cystic fibrosis (CF). Little is known about the routes of transmission of these pathogens from environmental or hospital sources to the patients. We hypothesised that strains of P. aeruginosa, B. cepacia complex and methicillin-resistant S. aureus (MRSA) are nosocomially acquired by CF patients. Bacterial isolates were obtained from 164 patients attending the CF Centre of Florence and from the hospital environment and the strains typed using restriction enzymes and pulsed-field gel electrophoresis (PFGE). Seventy (43%) of patients were colonised by P. aeruginosa, 6 (3.6%) by B. cepacia complex, and 11 (7%) by MRSA. Three P. aeruginosa strains were isolated from the sinks of the ward. All the MRSA isolates differed from each other. The analysis of 83 P. aeruginosa strains showed identical genotypes in five pairs of patients, whereas from the six patients infected with B. cepacia complex strains, two patients harboured identical genotypes. These pairs of patients had no contact with each other outside the CF centre and P. aeruginosa genotypes from the hospital environment differed from these clinical isolates, suggesting a possible common source of infection within or outside the centre. The study showed that, despite isolation precautions, a minimal risk of cross-infection still existed in the CF centre and that hygienic standards should be increased to further reduce this risk.     

Molecular epidemiologic analysis of Staphylococcus aureus isolated from four burn centers

Staphylococcus aureus has been a major cause of hospital-acquired infections. Methicillin-resistant Staphylococcus aureus (MRSA) has emerged since 1980s as an epidemiologic problem in hospitals. This old pathogen brings a new challenge to all physicians and bacteriologists. Hence, effective measures of MRSA control are in critical need. S. aureus or MRSA is one of the leading causes of infection among burn centers, resulting in a number of poor outcomes and even death. The present study performed a molecular epidemiologic analysis of S. aureus isolated from four burn centers in the southeast of China. A total of 85 isolates were collected, and molecular characters were determined for further investigation. In this study, the prevalent clone of MRSA among four burn centers was found to be SCCmec III (spa-type t030, agr I), which is resistant to 4 kinds of antimicrobials including erythromycin, clindamycin, kanamycin and mupirocin. Discrepancy between mecA detection and conventional tests used for MRSA identification was observed unintentionally. Our data demonstrated that the overall prevalence rate of MRSA was 55.3%, and drugs such as sulfamethoxazole/trimethoprim, linezolid and fusidic acid are efficient antibiotic options for treating S. aureus or MRSA infections among four burn centers studied in present investigation.     

The evaluation of nasal mupirocin to prevent Staphylococcus aureus burn wound colonization in routine clinical practice

BackgroundStaphylococcus aureus wound colonization frequently occurs in patients with burns and can cause impaired wound healing. Nasal mupirocin application may contribute to the reduction of burn wound colonization of endogenous origin, whereas colonization by the exogenous route can be reduced by blocking cross-infection from other sources. In this study we evaluated whether the implementation of routine treatment of patients and burn center personnel using nasal mupirocin ointment reduces S. aureus burn wound colonization.MethodsWe composed three study groups, consisting of a control period (Control), a mupirocin period (MUP), in which patients with burns were all receiving nasal mupirocin at admission, and a mupirocin + personnel period (MUP + P), in which we also screened the burn center personnel and decolonized S. aureus carriers by nasal mupirocin.ResultsThe patients who carried S. aureus in their nose and did not have S. aureus burn wound colonization at admission were considered as patients susceptible for the use of nasal mupirocin. In these patients, the S. aureus burn wound colonization rate was the same in all study groups. S. aureus nasal carriage was a significant independent risk factor for burn wound colonization (OR: 3.3; 95% CI: 1.4–7.6) when analyzed within the three study groups.ConclusionAlthough S. aureus carriage is a significant risk factor for developing burn wound colonization, the routine use of nasal mupirocin did not contribute to a reduction of burn wound colonization.     

Experimental colonization of vascular grafts with Staphylococcus aureus

In an attempt to solve the problem of infection of arterial grafts, the authors designed an experimental model to reproduce, in vitro, hematogenous seeding of grafts with Staphylococcus aureus. The inoculum, containing an average of 10(7) viable bacterial cells per millilitre, was circulated through grafts of various types. Normal dog aortas were used as controls. They entrapped a mean of 8 bacteria/cm2. The prosthetic grafts, previously placed in dogs as femorofemoral arteriovenous bypasses for 2 hours, trapped many more cells: expanded polytetrafluoroethylene, 23 cells/cm2; bovine heterograft, 607 cells/cm2 and Dacron velour, 2801 cells/cm2. All cell counts were significantly (p less than 0.001) different from control values. Thoracoabdominal aortic bypass grafts implanted in dogs 2 months previously gave the following mean numbers of trapped bacteria: expanded polytetrafluoroethylene, 19 122 cells/cm2; bovine heterograft, 863 cells/cm2 and Dacron velour, 3500 cells/cm2. Polytetrafluoroethylene had significantly (p less than 0.001) higher numbers of trapped bacteria than any other type of prosthesis. The bacteria were located mainly on irregular fibrin strands and on surface defects of the grafts. The addition of cefazolin during the seeding process at concentrations 10 to 25 times the minimal inhibitory concentration did not decrease the numbers of bacteria in any graft. Bacterial colonization of prosthetic arterial grafts depends on the graft material and on the duration of implantation, but this study provided no answer to the controversial question of how to prevent arterial graft infections with antimicrobial agents in patients who undergo vascular procedures that expose them to bacteremia.     

An outbreak of methicillin-resistant Staphylococcus aureus in a large medical center

The charts of 100 patients with methicillin-resistant, gentamicin-resistant Staphylococcus aureus (MSRA) were reviewed after an outbreak of MSRA occurred in our hospital. The location of the patients at the time of first positive culture was studied. The NICU was the most common location (24%). The burn unit accounted for nine per cent, and the remaining patients were widely distributed among the surgery services. Patterns of transmission were difficult to determine, and even with strict measures, complete eradication of the organism has not yet been achieved. Vancomycin, a potent and nephrotoxic antibiotic, is the treatment of choice.     

Childhood epistaxis and nasal colonization with Staphylococcus aureus.

OBJECTIVE: Epistaxis is very common in children but its cause remains unknown. We postulate that nasal colonization with Staphylococcus aureus leads to inflammation, crusting, and ultimately new vessel formation. STUDY DESIGN: A prospective case-control study. SUBJECTS AND METHODS: Sixty-seven children were recruited, 42 with epistaxis (22 had crusting in the nasal vestibule; 20 did not) and 25 control subjects. A microbiology swab was taken from the anterior nasal cavity of each child. RESULTS: All groups were equally likely to have a positive culture. S aureus was more common in the epistaxis group (P = 0.008) compared with the control group. There was no difference in the prevalence of S aureus between crust and noncrust groups. Epistaxis patients were much less likely to have isolates of respiratory pathogens or a skin commensal. CONCLUSION: Children with epistaxis are more likely to have nasal colonization with S aureus than controls. Our data would support the hypothesis that S aureus replaces existing nasal flora and causes inflammation and new vessel formation.     

瑞金医院烧伤中心甲氧西林耐药金黄色葡萄球菌同源性分析

目的从分子生物学水平分析甲氧西林耐药金黄色葡萄球菌(MRSA)在上海瑞金医院烧伤中心院内感染的流行状况。方法用 WHONET5统计软件分析2003—2005年瑞金医院烧伤中心 MRSA 的分布状况;用随机扩增多态 DNA(RAPD)技术对本中心住院患者临床标本中分离的17株 MRSA 进行同源性分析。结果分离的17株 MRSA 为同一 RAPD 型(引物为 ERIC2、RAPD7)。结论本中心多年来持续存在和流行的 MRSA 为同一个型别,应成为瑞金医院烧伤中心抗感染治疗和院内感染控制的重点菌株。     

Hospital infection and epidemiology of Staphylococcus aureus in a regional hospital. Value of sertyping

Staphylococcus aureus isolated from purulent material has been systematically submitted to seroagglutination by Pillet's method as from 1972 to 1976. 495 serotyped strains from 333 patients are considered in the spread of infection. Epidemiological incidence and antibiotic resistance of each serotype is evaluated. As a result a new approach has been introduced in the operating theatre and in the wards. Hospital serotypes tend to disappear and new serotypes appear less virulent.     

Experimental colonization of a polyester vascular graft with Staphylococcus aureus: a quantitative and morphologic study

Colonization of a polyester (Dacron) vascular graft by Staphylococcus aureus 209P-R was studied. Twenty-five dogs had thoracoabdominal aortic bypass. After intervals of 2 hours (three dogs), 8 days (five dogs), 1 month (six dogs), 2 months (six dogs), or 6 months (five dogs), a bacteremic challenge was produced by intravenous injection of 6 x 10(8) colony-forming units of S. aureus. Two hours later grafts were removed and cut into 10 fragments, each submitted to bacterial counts and scanning electron microscopic studies. Results of bacterial counts were expressed in colony-forming units (CFU) per square centimeter of graft segment (median [lower to upper quartiles]). Normal canine aortas (n = 2) used as controls trapped no bacteria. Colonization of Dacron grafts varied according to the duration of graft function (p less than 0.01): after 2 hours, 4416.5 CFU (1158 to 9073 CFU); after 8 days, 1515 CFU (963 to 2893 CFU); after 1 month, 199 CFU (86 to 538 CFU); after 2 months, 615 CFU (243 to 1407 CFU); and after 6 months, 1 CFU (1 to 5 CFU). Heavily colonized fragments were observed for duration of graft function of 2 months or less, whereas at 6 months all the fragments trapped fewer than 50 CFU/cm2 of graft segment. Scanning electron microscopy showed that colonization was closely associated with healing. Staphylococcal entrapment was related to the amount of fibrin deposits, which were especially abundant where the thrombotic matrix was unorganized and on bare polyester filaments. Graft colonization is especially to be feared in the first weeks after graft implantation, an observation which may help to define guidelines for preventing hematogenous vascular graft infection.     

Molecular epidemiology of methicillin-resistant Staphylococcus aureus in a burn unit from Brazil

Methicillin-resistant Staphylococcus aureus (MRSA) poses a threat for patients in burn units. Studies that mix epidemiological designs with molecular typing may contribute to the development of strategies for MRSA control. We conducted a study including: molecular characterization of Staphylococcal Chromosome Cassette mecA (SCCmec), strain typing with pulsed field gel electrophoresis (PFGE) and detection of virulence genes, altogether with a case–case–control study that assessed risk factors for MRSA and for methicillin-susceptible S. aureus (MSSA), using S. aureus negative patients as controls. Strains were collected from clinical and surveillance cultures from October 2006 through March 2009. MRSA was isolated from 96 patients. Most isolates (94.8%) harbored SCCmec type III. SCCmec type IV was identified in isolates from four patients. In only one case it could be epidemiologically characterized as “community-associated”. PFGE typing identified 36 coexisting MRSA clones. When compared to MSSA (38 isolates), MRSA isolates were more likely to harbor two virulence genes: tst and lukPV. Previous stay in other hospital and admission to Intensive Care Unit were independent risk factors for both MRSA and MSSA, while the number of burn wound excisions was significantly related with the former (OR = 6.80, 95%CI = 3.54–13.07). In conclusion, our study found polyclonal endemicity of MRSA in a burn unit, possibly related to importing of strains from other hospitals. Also, it pointed out to a role of surgical procedures in the dissemination of MRSA strains.     

Molecular characterization of multidrug-resistant (MDR) Pseudomonas aeruginosa isolated in a burn center

Objective

The aim of this study was to characterize molecularly multidrug-resistant (MDR) Pseudomonas aeruginosa isolates collected from burn center (BC) patients and environment in a hospital localized in Rio de Janeiro city, RJ, Brazil.

Influence of S. aureus and Str. pyogenes wound colonization on bacterial translocation in a burn model

Summary Bacterial translocation (BT) and release of endotoxin from the gut may contribute to septic complications in severely burned patients. In earlier experiments, it was shown in a burn model that BT exceeded the role of wound dissemination when burn wounds were colonized with Pseudomonas aeruginosa. Burn wound colonization with Pseudomonas aeruginosa also enhanced BT. It was concluded that endotoxin from gram-negative micro-organisms colonizing the burn wound appeared to play a role in the increased BT. In this study, the contribution of burn wound colonization with the gram-positive micro-organisms S. aureus and Str. pyogenes to BT and endotoxemia has been examined in Escherichia coli monoassociated mice with a 30% scald. The animals were sacrificed two days post-burn. The peritoneal cavity, the heart, one lung, the liver, the spleen and the cecum were cultured. Endotoxin in plasma was determined by means of the Limulus amoebocyte lysate assay. It appeared that dissemination of E. coli from the gut played a more important role than S. aureus or Str. pyogenes dissemination from the burn wound in this model. In only one of the 15 surviving Str. pyogenes contaminated animals dissemination had taken place from the burn wound. Dissemination of S. aureus was not seen in the S. aureus contaminated group. The incidence of E. coli translocation two days postburn, to the spleen (p<0.05) and liver (p<0.01) was enhanced in the Str. pyogenes group compares to the control group. Wound colonization by S. aureus did not increase the incidence of E. coli translocation. Endotoxemia was found in three of the 15 Str. pyogenes and in none of the S. aureus contaminated animals. In one of the 15 control animals, endotoxin was detected in plasma. These differences are not significant. The cause of the enhanced BT to the spleen and the liver in the Str. pyogenes contaminated group remains as yet unclear.Abbreviations BT bacterial translocation - SPF specific pathogen free - CFU colony forming unit - GI gastrointestinal - BHI brain heart infusion - LPS Lipopolysaccharide     

Topical use of lysostaphin for Staphylococcus aureus infection of burn wounds in mice]

The effect of lysostaphin on the burn wounds infected with Staphylococcus aureus was studied in mice. The results showed that the mortality and incidence of bacterial isolation in wounds were 17.2% and 8.3%, respectively, in mice treated by lysostaphin, and the figures were significantly lower than that treated by SD-Ag (40.6% and 100%) or base (44.1% and 94.7%). In lysostaphin group the bacterial count of subeschar tissue was 1325 cfu/g, compared with more than 10(9) cfu/g in both SD-Ag and base groups. The results demonstrate that lysostaphin has powerful killing effect on S. aureus, and may be used as atopical antimicrobial to control burn wound infection with S. aureus.     

Characteristics of burn patients at a major burn center in Shanghai

In China, burns are becoming a major cause of morbidity and mortality with large societal and economic implications. To date, there is little epidemiological data on burns in China to direct prevention efforts. This study describes the characteristics of burn patients admitted to a major burn center in Shanghai using a burn registry developed in Toronto, Canada. A retrospective review of burn patients discharged from the Shanghai's Rui Jin Hospital Burn Unit, between March 1st 2002 and April 30th 2003, was conducted. Of 527 patients discharged, 307 were acute burn patients and 302 (98.4%) had complete data to be included in the study. There were 214 (71%) males and 88 (29%) females with a male to female ratio of 2.4:1. The median age was 30 years, and the median total body surface area burned was 10%. The majority of burns occurred at work (58%), and the most frequent etiology was flames (39%) followed by scalds (31%) and contact with hot objects (15%). Sixteen (5%) patients had inhalation injury and six (2%) patients died. There were 70 (23%) children (0–14 years), 221 (73%) adults (15–59 years) and 11 (4%) seniors (60 years and above). Children had more scald burns (83%) and the majority (83%) occurred at home. Adults had more flame burns (46%) and the majority (79%) were work-related injuries. Seniors had more flame burns (73%) and the majority (55%) occurred in domestic incidents. Seniors had deeper burns (13%, p = 0.005), required more escharotomies (55%, p = 0.002), required more operations (2, p = 0.051) and had higher mortality (36%, p < 0.001) than other age groups. These results provide compelling evidence for performing population-based studies to identify risk factors that are susceptible to modification in each age group.     

Histopathological comparisons of Staphylococcus aureus and Pseudomonas aeruginosa experimental infected porcine burn wounds

Chronic skin wounds are a significant human health concern and are often complicated by infection with Pseudomonas aeruginosa and Staphylococcus aureus, particularly methicillin resistant S. aureus (MRSA). Translating the knowledge gained from extensive study of virulence mechanisms and pathogenesis of these bacterial species to new treatment modalities has been lacking in part due to a paucity of animal models able to recapitulate human disease. Our groups recently described a novel porcine chronic burn wound model for the study of bacterial infection; however, the histopathology of infection has yet to be described. The objective of this study is to define the histopathology of this model using important human chronic wound bacterial isolates. Porcine full‐thickness burn wounds topically inoculated with P. aeruginosa strain PAO1, MRSA S. aureus strain USA300 or both bacteria were used to define and quantify histopathologic lesions. The development of a systemic, well‐defined rubric for analysis allowed for evaluation of differences between infection groups. These differences, which included epithelial migration and proliferation, stromal necrosis, fluid accumulation and intensity and character of the innate and adaptive inflammatory cell responses, were identified temporally between infection groups. Mono‐species infected wounds developed a hyper‐proliferative wound edge. Coinfected wounds at day 35 had the largest wound sizes, increased amounts of neutrophilic inflammation, immaturity of the wound bed, and retention of necrotic tissue. Infection, regardless of species, inhibited wound contracture at all time points evaluated. Most importantly, this model recapitulated key features of chronic human wounds. Thus, this model will allow researchers to study novel treatment modalities in a biologically relevant animal model while monitoring both host and bacterial responses.     

The epidemiology of toxemic infections caused by Staphylococcus aureus in an intensive care setting

The mission of the National Reference Centre for Staphylococcal Toxemia (CNRTS) is to participate in the epidemiological surveillance of staphylococcal toxemia in France. As these syndromes do not have to be declared, the data collected remain incomplete. Comparison of the clinical data with the results of molecular analysis of the causal strains has nonetheless enabled advances in our understanding of the present-day epidemiology of these syndromes, a clearer knowledge of their pathophysiology and isolation of a hitherto unknown entity, staphylococcal necrotizing pneumonia.     

Experimental colonization of an expanded polytetrafluoroethylene vascular graft with Staphylococcus aureus: a quantitative and morphologic study

We developed an animal model to reproduce hematogenous seeding of vascular grafts with Staphylococcus aureus. Expanded polytetrafluoroethylene (ePTFE) grafts were implanted in 41 dogs as thoracoabdominal aortic bypasses for six durations of implantation between 2 hours and 6 months. The inoculum containing an average of 10(8) viable bacteria/ml was then injected intravenously in 1 minute. Normal dog aortas were used as controls. They entrapped very few bacteria (0.7 +/- 1.7 colony-forming unit [CFU]/cm2). Colonization of ePTFE grafts was maximal after 2 hours of implantation (589 +/- 733 CFU/cm2). Bacterial entrapment decreased after 2 days (225 +/- 315 CFU/cm2, p less than 0.001) and 8 days (70 +/- 115 CFU/cm2, p less than 0.001) of implantation, but it was similar after 8 days, 1 month (83 +/- 90 CFU/cm2), or 6 months (93 +/- 143 CFU/cm2) of implantation. Colonization of ePTFE measured after 2 months of implantation (371 +/- 591 CFU/cm2) was significantly higher (p less than 0.001) than after 1 or 6 months of implantation. More than 500 CFU/cm2 were seen in 37% of the prosthetic fragments tested after 2 hours of exposure to blood; 99% of the fragments tested after 6 months of implantation trapped less than 500 CFU/cm2. Scanning electron microscopy showed that staphylococci were mostly seen on native fibrin deposits, particularly after 2 hours and 2 months of implantation. That persistent susceptibility of a flow surface devoid of endothelium to hematogenous bacterial colonization has to be taken into account to prevent delayed graft infections. Furthermore, it would be important to compare the ePTFE with other types of grafts whose healing phenomena are different.